1. Field of the Invention
This invention relates to apparatus for dumping mine cars and more particularly to apparatus which will without the control of an operator move a top-dumping mine car from its upright position to a dumping position and return the car to the upright position without reversing the power system driving the apparatus.
2. Description of the Prior Art
Top-dumping mine cars and many ladles for hot metals have an open-topped body mounted to rotate about a horizontal axis extending longitudinally of the car near its lower end. The cars have a connection point for a hoist chain at the side of the car opposite the axis of rotation. Ordinarily, the connection point is near the bottom of the car. The hoist chain extends from a motor driven windlass or drum located above the mine car and is connected to the mine car at the connection point. The windlass is rotated to shorten the chain and thereby rotate the mine car about its pivot until the center of gravity of the car swings past a line extending vertically from and above the axis of rotation, after which gravity causes the car to continue rotation to dump its contents through the open top. The maximum amount of rotation is limited either by the hoist chain or by a suitable stop. After the car is emptied, it is rotated in the opposite direction by means of the hoist chain to swing the center of gravity past the line extending vertically above the axis of rotation. Thereafter, gravity returns the car to the initial upright position.
In the apparatus heretofore available, it was necessary to reverse the direction of the motor driving the windlass four times during a cycle. As the car is tilted from the upright position to swing the center of gravity past the line vertically above the axis of rotation, the windlass is driven in a direction to shorten the length of the chain extending from the windlass. After the center of gravity passes the line extending from the axis of rotation and gravity will then cause continued rotation of the car, the direction of the rotation of the drum is reversed to lengthen the chain and allow rotation to continue to a point at which the contents can be dumped from the car through its open top. When dumping is completed, the direction of rotation of the drum is reversed to shorten the hoist chain and cause rotation of the car in the opposite direction to move the center of gravity of the car back over the line extending vertically from the axis of rotation. The direction of rotation of the drum is then again reversed to allow lengthening of the hoist chain and continued rotation of the car to its normal upright position. When dumping of the next car is begun, the direction of rotation of the drum is again reversed.
The center of gravity of the mine car will vary as the amount of ore in the car changes. The center of gravity of a car will be generally along the vertical center line between the axis of rotation and the point of attachment of the hoist chain. If the car is full of ore, the center of gravity will be higher in the car than when the car is empty. Variations in the location of the center of gravity cause variations in the degree of rotation necessary to cause the center of gravity to swing over a line extending vertically from the axis of rotation. If the ore in the car is sticky, only a portion of the ore may fall from the car when it is in the inverted dumping position. If dumping of the car is incomplete, it will then be necessary to rotate the car farther to swing the center of gravity over the line vertically above the axis of rotation to return the car to the upright position than if the car should be completely emptied. Conversely, less rotation from the upright position in which a car is delivered to the unloading station will be required to cause rotation to proceed by gravity if the car is completely filled rather than partially filled. Heretofore, control of the dumping operation has been by a skilled operator who utilizes the momentum of the rotating car to cause the center of gravity to swing through a vertical line through the axis of rotation. The operator utilizes his skill and experience in deciding just when to stop and reverse the direction of rotation of the windlass.
In U.S. Pat. No. 425,607 of W. W. Green, a mine dump car is operated by chains connected to each side of the dump car near its lower end. The chains pass over winding drums mounted above the car which shorten the effective length of the chain connected to the dump car to tilt it into a dump position. In the apparatus described in the patent, the position of the drum can be varied laterally to improve the angle of lift of the chain as the axis of rotation of the car is changed from one side to the other. The direction of rotation of the winding drum must be reversed as described above.
U.S. Pat. No. 2,393,695 of Kling illustrates apparatus for tilting a ladle in which a hook is adapted to be connected to the ladle near the bottom thereof at the side opposite the axis of rotation. The hook is suspended from a pulley which is made to move along a track which extends upwardly and laterally to rotate the ladle and cause molten metal in the ladle to flow from the upper end of the ladle. The ladle is brought back to its upright position by reversal of the motor causing movement of the pulley along the track.